If you strongly desire the idea of elevated lines but you can not fit in the additional 6" of height due to a knee wall, then consider just making the entire main deck 6" lower.
Also, instead of a raised section consider a subway tunnel to cross a mainline under instead of over another one.
If you are using section track consider using flex track just for the cosmetic curve. In my experience, the MTH Scale Trax makes the easiest to install 3 rail cosmetic curves. I have used Atlas 3r flex but it is stupid difficult to work with. GG bends nicely against templates for fixed curves but tends to be kinky for cosmetic curves and takes a while to work it for a smooth ultra gentle curve.
For cosmetic curves I use 800" and 1100" radius templates.
